Sharif Digital Repository

To overcome the problem of magneto hydrodynamic instabilities at the aluminum-cryolite interface in aluminum reduction cells, the use of a simple and efficient model has been suggested. In this paper a new model for evaluation of magneto hydrodynamic instabilities in aluminum reduction cells is proposed. This model is in the form of a wave equation for interfacial oscillations and is constructed based on Shallow Water approximation and linear stability analysis. In this model two terms for linear friction in each molten layer of aluminum and cryolite has been considered and also Lorentz forces in cryolite layer have not been neglected. By accounting of these additional terms in our model,... 

This paper presents a risk-based approach for evaluating the participation strategy of a battery storage system in multiple markets. Simultaneous offering in day-ahead energy, spinning reserve, and regulation markets is considered in this paper. The uncertainties considered include predicted market prices as well as energy deployment in spinning reserve and regulation markets. A new nonprobabilistic model is introduced in this paper to handle the uncertain nature of spinning reserve and regulation markets. Robust optimization is implemented to model these uncertain parameters and manage their related risk. The proposed risk-based model is a max-min problem, which is converted to its... 

Due to the increasing usage and capabilities of smart devices, mobile application developers build a large number of resource intensive applications, such as WAR applications. Even with the rapid development in hardware technology, the computing capability and battery capacity on wearable devices and smartphones still cannot meet the application demands with heavy computations and high battery drain. Pervasive computing addresses this problem by migrating applications to the resource providers external to mobile devices. The profitability of this method heavily depends on how to implement it and when to use it. Although there are many computation offloading systems proposed in the... 

This paper presents a decentralized load sharing and power management method for an islanded microgrid composed of PV units, battery units and hybrid PV/battery units. The proposed method performs all the necessary tasks such as load sharing among the units, battery charging and discharging and PV power curtailment with no need to any communication among the units. The proposed method is validated experimentally  

Lead-acid battery is a storage technology that is widely used in photovoltaic (PV) systems. Battery charging and discharging profiles have a direct impact on the battery degradation and battery loss of life. This study presents a new 2-model iterative approach for explicit modelling of battery degradation in the optimal operation of PV systems. The proposed approach consists of two models: namely, economic model and degradation model which are solved iteratively to reach the optimal solution. The economic model is a linear programming optimisation problem that calculates the optimal hourly battery use profile based on an assumed value of the battery degradation cost. The degradation model,... 

We study the problem of joint information and energy transfer in a two-hop channel with a Radio frequency (RF) energy harvesting relay. We consider a finite battery size at the relay and deterministic energy loss in transmitting energy. In other words, to be able to send an energy-contained symbol, the relay must receive multiple energy-contained symbols. Thus, we face a kind of channel with memory. We model the energy saved in battery as channel state with the challenge that the receiver does not know the channel state. First, we consider the problem without any channel noise and derive an achievable rate. Next, we extend the results to the case with an independent and identically... 

In a wireless powered communication network, an energy access point (EAP) supplies the energy needs of the network nodes through radio frequency wave transmission, and the nodes store the received energy in their batteries for their future data transmission. In this paper, we propose an online stochastic policy that jointly controls energy transmission from the EAP to the nodes and data transfer among the nodes. Our proposed policy is designed using a quadratic Lyapunov function to capture the limitations on the energy consumption of the nodes imposed by their battery level. The proposed policy is adaptive to different channel statistics of the network. We provide theoretical analysis for... 

In this paper, a new method is proposed utilizing a diversity scheme to reduce power consumption in large scale sensor networks. Sensor networks are composed of large number of battery powered nodes. Energy consumption is the most important design objective in sensor networks while delay and throughput are taken less into account. Wireless transmission is the other important characteristic of these networks. Small-scale fading decreases wireless communication performance. In a fading channel higher SNRs is needed and consequently more energy is consumed in fading channels. Another important characteristic of sensor networks is the necessity of fault tolerant protocols. Node-to-node links are... 

The present study was aimed at performance and energy analysis of a hybrid wind-hydrogen power system. Such system consists of wind turbines, batteries for the short time energy storage, electrolyzer, fuel cell and hydrogen tank for long time energy storage. The proposed configuration is used to supply energy demand of a region with discrete seasonal wind speed regime. Temporary wind energy profiles restrict using batteries for electricity storage as they lose much electrical stored energy for the long time. Based on direct wind turbine usage, batteries and hydrogen storage, different energy supply strategies are introduced and analyzed to power the household electricity demand. The energy... 

The rapid growth in use of renewable intermittent energy resources, like wind turbines (WTs) and solar panels, in distribution networks has increased the need for having an accurate and efficient method of handling the uncertainties associated with these technologies. In this paper, the unsymmetrical two point estimate method (US2PEM) is used to handle the uncertainties of renewable energy resources. The uncertainty of intermittent generation of WT, photo voltaic cells, and also electric loads, as input variables, are taken into account. The variation of active losses and imported power from the main grid are defined as output variables. The US2PEM is compared to symmetrical two point... 

In this paper a novel structure of a zero- voltage transition PWM boost converter is proposed. The main switch and diode of the converter are turned on and off under zero voltage transition. In addition the auxiliary switch and both diodes operate in ZCT condition. The auxiliary circuit consists of a transformer, a snubber capacitor and two diodes. Without imposing much current stress, the switching loss reduces significantly. So a higher efficiency converter is achieved. The simple structure and a wide range of operating current are the advantages of the proposed converter, which make it useful for solar battery chargers etc. The operation principles of the proposed converter are explained... 

The present work describes the preparation and electrochemical characterization of RuO2/MWCNT/Stainless Steel Mesh (SSM) electrode as compared with a MWCNT/SSM electrode in the positive half-cell of a Vanadium Redox Flow Battery (VRFB). The electrochemical characterization of prepared electrode was carried out using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge procedures. The electrochemical activity of MWCNT/SSM modified with RuO2 as positive electrode in a VRFB was notably improved. The RuO2-included electrodes demonstrated high peak current ratio, small peak potential difference and high electron... 

Discharge characteristics of nanorods (NRs), microsized and nanosized copper (II) oxide (CuO) particles prepared via thermal decomposition and thermal oxidation routes are examined as cathode materials of a Zn/CuO cell without membrane separators. The electrochemical discharge is examined galvanostatically at a current density of 500 mAg−1 and reveals that the first discharge cycles of all the CuO materials contain one potential plateau; subsequent discharge cycles involve three potential plateaus. Each potential plateau is due to an electrochemical reaction. The first, second, and third potential plateaus are attributed to Cu2O3, CuO, and Cu2O discharges,... 

Two and three dimensional modeling of a single cell of vanadium redox flow battery has been done thoroughly according to electrochemical and fluid mechanic equations in this study. The modeling has been done in stationary state and its results have been presented in three chemical, electrical and mechanical sub models. The parametric analysis on some of important factors in cell operation demonstrated that increase in electrode and membrane conductivity and electrode porosity contributes to electric potential increase in cells. Also operational temperature increase leads to decrease in cells' voltage. Better fluid distribution on the electrode surface area results in better cell operation,... 

Na3MnCO3PO4 (NMCP) particles were synthesized via ball milling of Mn(NO3)2.4H2O, Na2HPO4.2H2O and Na2CO3.H2O powders. The particles were anchored onto reduced graphene oxide (rGO) sheets during hydrothermal reduction process under stirring. Materials produced were characterized by x-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), thermogravimetric (TG) measurement and galvanostatic charge/discharge tests. Results showed that dissolution of ball milling products in DI water is an effective method for separation of NMCP from byproducts. Best milling time for production of pure NMCP of minimum particle... 

This paper concentrates on degradation of electric vehicle (EV) lithium-ion batteries in vehicle-to-grid (V2G) programs and proposes a practical wear cost model for EVs charge scheduling applications. As the first step, all the factors affecting the cycle life of lithium-ion batteries are identified and their impacts on degradation process are investigated. Subsequently, a general model for battery loss of cycle life is devised incorporating all the pertinent factors associated with charging and discharging activities in V2G applications. Modeling the battery wear cost as a series of equal-payments over the cycle life, a mechanism for calculating the cost incurred by EV users due to... 

It has been attempted to gain a new viewpoint in transient cell modeling of vanadium redox flow battery. This has been achieved by considering electrochemical relations along with conceptual electrical circuit of this kind of battery. The redox flow battery is one of the best rechargeable batteries because of its capability to average loads and output power sources. A model of transient behavior is presented in this paper. The transient features are considered as the most remarkable characteristics of the battery. The chemical reactions, fluid flow, and electrical circuit of the structure govern the dynamics. The transient behavior of the redox flow battery based on chemical reactions is... 

Plug-in hybrid electric vehicles draw electricity from the electrical grid and store energy in their batteries. To increase charge availability for plug-in hybrid electric vehicles, on-board chargers can be used, which should be small in size and lightweight. In this article, an on-board bidirectional soft-switched battery charger is proposed that utilizes a phase-shift-controlled dual-bridge series resonant converter with isolation. The bidirectional characteristic of proposed charger makes it suitable for vehicle-to-grid operation (i.e., injecting power from the vehicle to the grid) in smart grids. A switching control scheme is also proposed to provide soft-switching operation for all... 

There is a global tendency towards using Distributed Generation (DG) and renewable energy resources. Considering low utilization cost and low undesirable environmental effects, wind farms have become a considerable resource for producing electrical energy in many countries. Since Wind farms are not programmable and their power output which depends on weather and wind speed is uncertain, they create problems for utilizing electricity system. There are different methods for preserving system stability against the uncertainty of wind power plants. Optimal utilization of pumped storage and gas resources is one of the approaches for reducing production risk of wind farms. In this paper, it is...